(5.2.2)
Consider the Iberic stock (Div. VIIIc e IXa) of fourspot megrim, Lepidorhombus boscii.
The following parameters were estimated by the Working Group of ICES (ICES, 1998b):
Natural Mortality Coefficient: 
M = 0.20 year^{1} 


Fishing mortality in 1996: 
F_{96} = 0.36 year^{1} 
Exploitation pattern:
Age 
1 
2 
3 
4 
5 
6 
7+ 
s_{i} 
0.06 
0.43 
0.89 
1.65 
1.66 
1.22 
1.22 
Mean weight (kg) in the catch and in the stock:
Age 
1 
2 
3 
4 
5 
6 
7+ 
0.037 
0.067 
0.086 
0.109 
0.144 
0.188 
0.244 
1. Adopting the value 1000 for the recruitment to the fishing area, calculate the longterm annual catch in weight, the annual mean biomass, and the annual mean weight in the catch, corresponding to the fishing mortality level of 1996.
2. Adopting the factor F_{factor} between 0 and 2.5 year^{1} with intervals of 0.1 year^{1} draw the curve of the annual catch in weight against F_{factor}. Represent, in the same graph, the curve of the mean biomass against F_{factor}.
3. Calculate the biological reference point F_{0.1}
4. Calculate the biological reference point F_{max}
5. In the graph of the curves of the annual catch in weight and of the mean biomass against F_{factor}, mark the Biological reference points F_{0.1} and F_{max} which were previously calculated. Make your comments.
6. Calculate the longterm mean biomass, the catch in weight and the mean weight in the catch for F_{0.1}. Compare those characteristics with the values obtained in question 1 and make your comments.